instaleing a new cieling

we have 10ft ceiling in the kitchen and living room and we are lowering them too 8ft and we are just woundering if we have too in insulat the lowed ceiling when the excieing ceiling is fully insulaed already

instaleing a new cieling

Having two insulation systems interrupted by a large air void could be setting yourself up for moisture condensation issues. You would be creating an unvented plenum. If the air temperature in that space ever drops below dew point, get ready for a host of problems. You'd be better to lower the insulation system down to ceiling level and vent above it.